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Biology > Required practicals > Flashcards

Required practicals Flashcards

1
Q

How could you assess the reliability of your results?

A
  • Carry out statistical test
  • Work out standard deviations and plot these on a graph, SD shows the variation around the mean
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2
Q

Why is % change in mass used rather than actual change in mass?

A
  • Objects may not have the same starting mass
  • Allows you to compare results
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3
Q

Describe some asceptic techniques when handling a solution of E.coli.

A
  • Clean surfaces using antiseptic wipes
  • Use a sterilised pipette to transfer the E.coli
  • Close all of the lab windows and doors
  • Clean hands before and after handling the bacteria
  • Have a bunsen burner in the area, produces convection current of heat to kill any bacteria
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4
Q

Why is the bacteria incubated at 25°C?

A
  • To stop harmful bacteria from growing
  • These would grow best at human body temperatures (37°C)
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5
Q

How can you compare the effectiveness of different antibiotics applied to the same bacteria?

A

Calculate the area of the zone of inhibition by measuring the diameter of the clear zone on the agar.

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6
Q

Why should the lid of the petri dish not be completely sealed?

A
  • Culture given access to some oxygen
  • Stops harmful anaerobic bacteria growing
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7
Q

How is the rate of reaction calculated from time in the rate of an enzyme controlled reaction involving trypsin and milk?

A

1/time

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8
Q

Outline the practical procedure used to measure the effect of temperature on enzyme activity, using trypsin and milk.

A
  • Immerse equal volumes of tyrpsin and milk, in different test tubes, in a water-bath for 5 minutes
  • Mix together the two test tube contents and immediately start timing, record the time it takes for the milk to be completely hydrolysed (colourless or the same colour as the control standard)
  • Test at least 5 temperatures and repeat 3 times for each in order to calculate a mean time at each temperature.
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9
Q

How is a control set up in a practical measuring enzyme activity?

A
  • Replace the enzyme solution with distilled water or boiled enzyme solution
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10
Q

Describe how you would make a temporary mount of a piece of plant tissue to observe the position of starch grains in a cell.

A
  • Add a drop of water to the slide
  • Place a thin sample of plant tissue to the slide
  • Add some drops of potassium iodide
  • Slowly lower a cover slip using a mounted needle at an angle to ensure no air bubbles form
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11
Q

Describe the procedure to prepare a root tip slide.

A
  • Cut a root tip using a scalpel and place in hot HCl. Leave for 5 minutes.
  • Remove from HCl and rinse with distilled water
  • Cut the tip of this sample using a scalpel and place on slide
  • Add a few drops of stain (toluidine blue) to make chromosomes visible
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12
Q

Where in plants can cells undergoing mitosis be found?

A

Meristem tissue at shoot and root tips.

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13
Q

What is the mitotic index? State the formula.

A

The ratio of cells in sample undergoing mitosis.
Number of cells with visible chromosomes divided by the total number of cells

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14
Q

How would you estimate the water potential of a potato sample?

A
  • Produce sucrose solutions of different concentrations
  • Cut equal volume/shaped cylinders of potato and measure the initial mass of each one
  • Place each one in a different conc. solution and leave for 2 days
  • Remove potatoes, pat dry with paper towel and reweigh
  • Calculate change in mass and % change in mass
  • Plot calibration curve of sucrose solution concentration by % change in mass
  • Draw line of best fit and find the concentration of sucrose solution when % change in mass is equal to 0
  • Use data from an outside source to find the water potential at this concentration
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15
Q

State 2 factors which affect the permeability of a cell membrane.

A
  1. Temperature
  2. Concentration of solvent (ethanol)
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16
Q

How can beetroot be used to measure thechanges to the permeabilty of a plant cell membrane?

A
  • Red pigment leaves as the cell membrane becomes more permeable
  • Colorimetry can be used to determine a quantitative measurement (absorbance)
17
Q

How does temperature impact the beetroot cell membrane permeability? Explain

A
  • Hotter temperature makes cell membrane more permeable as protein channels and carrier proteins denature (tertiary structure)
  • Freezing temperature will cause increase in permeability as ice will pierce and damage the cell membrane
18
Q

Outline the procedure of using chromotography to seperate photosynthetic pigments.

A
  • Draw a horizontal line 1cm above the bottom of the TLC paper using a pencil
  • Add some acetone and plant leaves and grind up using a pestle and mortar to release the photosynthetic pigments
  • Use a capillary tube to transfer this pigment onto the pencil line
  • Suspend paper in solvent and leave the paper until the solvent has run up around 3/4 of the paper
  • Remove and mark on pencil where the solvent has reached
  • Calculate Rf value for each spot
19
Q

What is the function of dehydrogenase enzyme in photosynthesis?

A

Catalyses the accpetance of electrons on the final electron acceptor (NADP) in the LDR, or in the experiment this is DCPIP

20
Q

What is the colour change of DCPIP and how does this appear in the plant solution?

A

Blue to colourless (when reduced)
Blue-green to green

21
Q

Why is the plant extract chilled in an ice-cold bath?

A

Slows down hydrolytic enzyme activity which could break down chloroplasts

22
Q

How do you set up the control when investigating the activity of dehydrogenase enzyme in photosynthesis?

A
  • Fill cuvette with distilled water and chloroplast extract
23
Q

How is light intensity and wavelength changed when measuring the rate of dehydrogenase activity?
What is controlled?

A

Light intensity = distance of lamp from sample
Wavelength = use different colour filters, filter will absorb all other light and reflect the visible colour

Carry out in dark room where there is no other light source.

24
Q

What will be the least effective filter in the investigation into dehydrogenase activity during photosynthesis and why?

A

The green light filter
- Only green light is reflected
- Chlorophyll does not absorb green light well
- Therefore there is less light available for the LDR, less chlorophyll becomes oxidised and less elctrons transferred down the ETC

25
Q

What stats test can be used to analyse the results of a simple animal response investigation involving a choice chamber and why?

A
  • Chi squared test
  • Investigating the difference between expected and observed frequencies
26
Q

What is the conclusion when the calculated stats test value is greater than the critical value?

A
  • We reject the null hypothesis
  • There is a less than 5% propability that the differences/correlation is due to chance.
  • There is a statistically significant difference/correlation
27
Q

What is the hazard and precaution for the investigation into simple animal responses?

A
  • Animals (insects) are a biohazard
  • Wash hands before and after handling
28
Q

How can you use Benedict’s solution to measure the concentration of glucose in an unknown solution?

A
  • Add Benedict’s solution to known concentrations of glucose and heat
  • Measure absorbance using a colorimeter
  • Produce a calibration curve of known concentrations of glucose solution and absorbance
  • Add Benedict’s solution to unknown and heat, measure absorbance and compare to calibration curve
29
Q

How can you increase the accuracy of your calibration curve?

A

Take more readings, more concentrations of glucose/sucrose solution

30
Q

Outline the procedure for the investigation into the effect of different variables on species distribution.

A
  • Use a random number generator (on calculator) to generate a set of coordinates (at least 10 sets)
  • Use two tape measures to create a set of axes for these coordinates in the sample area
  • Place a quadrat at each coordinate that is generated, place the bottom right corner at this coordinate each time
  • Record the % cover for the chosen species and a named variable (light intensity, pH) at each coordinate
31
Q

When is median used to process data instead of meam? (2)

A
  • Small sample
  • Presence of outliers/anomalies

Biology (10 decks)

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